Call signaling system



Oct. 5 1926. 1,601,969

J. 5. JAMMER CALL SIGNALING SYSTEM Filed Dec. 29, 1920 //7Ve/770/' Jacob5 Jam/War:

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Patented Oct. 5, 1926,

UNITED STATES PATENT OFFICE.

JACOB S. JAMMER, OF NEW YORK, N. Ys, ASSIGNOR TO WESTERN ELECTRICCOMPANY,

INCORPORATED, OF NEW YORK, N. Y., -A CORPORATION OF NEW YORK.

.CALL SIGNALING SYSTEM.

Application filed December 29, 1920. Serial No. 433,747.

This invention relates to a call signaling system and-particularly to ameans for call s gnaling over a carrier current transmis- SlOIl system.

A principal object of the invention is to transmit call signal impulsesover a carrier wave transmission system.

A more specific object of the invention is to transmit call signalimpulses over an intelligence communication system of the modulatedcarrier current type by changing the carrier frequency from the valuenormally used for intelligence communication.

A furtherobject of the invention is to provide a signal system adaptedto be used in carrier current systems in which means are provided forpreventing interference with the signal by a simultaneously actuat'edintelligence transmitting means.

The invention, which is applicable gener. ally to carrier currentsystems, consists in essence in operating call signal apparatus at areceiving station by carrier waves transmitted from a transmittingstation and differing in frequency from the carrier frequency of wavesmodified in accordance with messages and transmitted between the samestations. Where the carrier wave for transmitting messages iscontinuously transmitted, as in the so-called closed circuit carrierwavecommunication systems a calling signal may be transmitted bychanging the frequency of this carier wave to the different carrierfrequency used for calling. The calling signal receiving apparatus willaccordingly be made to respond whenever this change occurs in thefrequency of'the normally transmitted message carrier wave.

The word signaling, as used throughout the specification, isdistinguished from intelligence communication and signal is used todenote a ringing or calling means. The expression intelligencecommunication which has sometimes been given a broad meaning, limitedonly by the literal signification ofthe words, will be used here toexclude the merecalling or signalling .and will include within itsmeaning telesystem whatever and accordingly may be used in a simplex ormultiplex system and in wire or radio systems.

' The invention, the general features of which have been describedabove, will now be described in detail in connection with a preferredsystem which has been illustrated by a drawing, the single figure ofwhich shows the circuits of a complete two-way transmitting andsignaling unit of a multiplex transmission system.

In the drawing there are shown the necessary circuits which would enableone to con duct a complete two-way conversation from low "frequency lineL over the carrier line ML to a distant station, and to transmit andreceive ringing signals over the carrier line. In a practical case theline L would be a subscribers loop andsome of the operations which, forsimplicity, will be indicated as originating in the low frequency linewould be performed by a central station operator. The circuits mayterminate in a carrier line as shown, or in a radiating conductor in thecase of a radio system, the terminal cirouit arrangements for modulatedcarrier transmission being equally applicable to each.

Describing first the circuits for intelligence communication, thecarrier line ML terminates in a balancing network MN to which it isconnected by the series windings 2 of the balanced transformer or hybridcoil 1. With a condition of balance established, the high frequencytransmitting and receiving circuits connected respectively with theseries windings and bridge circuit of the hybrid coil, are completelyconjugate to each other with respect to line ML.-

There is a similar low frequency balanced transformer and networkarrangement 3 for the purpose of connecting the low frequencytransmitting and receiving circuits to the low frequency line L.

Oscillation generator G is representative of various types that may beused, the only essential feature for the purpose of this invention beingthe inclusion of a frequency determining circuit a by the adjustment ofthe reactive elements of which the frequency of the generator may bevaried.

The generator has the usual inductive coupling between the input andoutput circuits. Batteries BA and BB, respectively supply energy to thefilament and to the space circuit a speech modulated carrier wavecomprising upper and lower sidebands and also to transmit some energy ofthe carrier wave frequency without modulation. The band filter TF may beof the well known Campbell type which has been described in Patent No.1,227,114 atented May 22, 1917. As here used the filter is designed topass the unmodulated carrier frequency component and one side band whichare transmitted to line ML through balanced network system 1. Referencenumeral 6 indicates addi tional transmitting channels.

Carrier current modulated by telephonic frequency currents. is receivedover line ML and is transmitted through the balanced network and throughthe band filter RFto detector D, filter RF being similar to filter TF.Reference numeral 7 indicates circuits of additional receiving channelsfor multiplex operation. It should be noted that filter TF functions toprovide the necessary selectivity in multiplex operation as well as tosuppress one of the side bands, filter RF functioning similarly.

The detector or demodulator functions in the usual manner to produce lowfrequency currents of the same character as those used at the distanttransmitter to modify the transmitted carrier wave. The detector also.operates to a degree as an amplifier of the received high frequencycurrent and accordingly transmits corresponding high frequency wavesfrom its output circuit whenever high frequency waves are received. Thedetected currents are amplified by amplifier A and transmitted bytransformer 8 to circuit 9 in which low pass filter RF suppresses thehigh frequency components and permits only waves of telephonicfrequencies to pass. Currents of telephonic frequencies are transmittedthrough balanced circuits 3 to an indicating device (not shown) in lineL.

Considering now the signaling feature of the invention, low frequencysignaling impulses, as from a 16 cycle source, are transmitted over lineL. This current is picked up by tuned circuit 10 which thereforeconstitutes a substantial short-circuit of the line for currents of thisfrequency and prevents the modulation of the carrier wave thereby.

A .relay in tuned circuit 10 actuates a circuit closer which energizesthe relay 11. This relay closes a circuit through condenser 12 andplaces this condenser in parallel with condenser 13 and accordinglyincreases the total capacitance of the circuit 4. This func tion isdesirable in the case that the lower side band is normally transmittedsince it results in a decrease in the carrier frequency. The changedfrequency carrier wave may be made to occupy substantially the middleportion of the normally transmitted frequency band. If the filter TF, onthe other hand, is designed .to transmit the unmodulated carrier wavecomponent and upper side band, it is desirable to decrease thecapacitance in circuit 4 and this may be accomplished by changing theposition of switch 14. In this alternative operation, the relay contactis so' adjusted that the circuit is normally closed through 12 and isopened by relay 11.

The changed carrier frequency current is transmitted through filter TFand balanced network circuits 1 to the distant station. Since thecircuits for receiving the signals at the distant station are identicalwith the receiving circuits at the station shown, they will be describedwith reference to the latter station. The received signaling currentpasses through the circuits 1 and band filter RF to detector D. Therebeing only a single frequency, the current is transmitted unchanged,except as it may incidentally be amplified, to amplifier A. The tunedcircuit 15 is resonant to the changed carrier frequency and hence thiscircuit picks up the signal current and transmits it by means oftransformer 16 through secondary tuned circuit 17 to thermionic relaydevice R.

., Tuned circuit 15 is sufiiciently selective to discriminate betweenthe normal and changed carrier frequency and it will not respond to theside band frequencies, the amplitudes of the currents corresponding towhich are small as compared with that of the changed frequency signalwave. Accordingly, tuned circuit 15 will be practically unaffected bythe transmitted currents during normal message transmission. Relay Roperates in a well known manner to produce a change in its space currentduring reception of the changed frequency carrier current and the changein space current is sufficient to cause relay 18 to operate. Relay 18closes the circuit of relay 19 which disconnects the low frequencycircuit L from the two-way channel and connects it to a local ringingsource as shown.

Although the invention has been specifically described with reference toa carrier telephone system, it should be understood, as has beenexplained above, that it is not so limited in application but may beused, as well, in a carrier telegraph system or, conceivably in acarrier current system adapted for power transmission. It should furtherbe understood that it is not limited in scope to use in an intelligencecommunication system,to the particular system shown, or even to wiretransmission, but only by the appended claims.

What is claimed is:

'1. In a modulated carrier current transmission system in which thetransmitted band consists of the unmodulated carrier frequency componentand one side band, the method of signaling which includes the steps ofchanging the carrier frequency to substantially the centre of saidtransmitted band and selectively indicating the currents of said changedcarrier frequency.

2. A transmission system compr sing a transmitting station, a distantreceiving station having a controlled device and message receivingmeans, means at said transmitting station for normally transmitting tosaid receiving station a wave of a given frequency, means for modifyingsaid wave to transmit messages, means for changing the frequency of saidtransmitted wave, means at said distant station for demodulating saidmessage-modified wave, and means coupled to the output of saiddemodulating means responsive only to .said wave of changed frequency tooperate said controlled device.

3. In a signaling system comprising a transmitting station and a distantreceiving station, a source of carrier current, means for modifying saidcarrier current in accordance with messages and for transmitting fromsaid transmitting station to said distant receiving station the carriercurrent so modified, means at said distant station for detecting thereceived carrier current and indicating said messages, means forshifting the fequency of-said carrier current whereby signalingindications may be trans mitted over said system, means at said distantstation for selecting from said detecting means the incoming current ofshifted frequency and for rectifying it, and a signal operated by therectified current.

4. In a signaling system, a high frequency energy transfer clrcuit,means included .in

said transfer circuit for supplying low fre-' quency modulated carrierwaves and for changing the frequency of the carrier waves, a lowfrequenc circuit, means interconnect:

ing said circuits comprising demodulating" apparatus wherebylowfrequency impulses may be transmitted to said low-"frequency circuitcorresponding to the modulations of a particular high frequency carrierwave,

and resonant circuit means connectedin energy transfer relation to theoutput circuit of said demodulating apparatus responsive only to achanged carrier frequency.

5. In a signaling system, a high frequency circuit, a law frequencycircuit, source of carrier current, means whereby modulated carriercurrent may be transmitted over said high frequency circuit,demodulating means interconnecting said circuits, means for changing thecarrier frequency of the transmitted current, a selective circuitconnected in energy transfer relation with the output of saiddemodulating means responsive only to the changed carrierfrequencycurrent, and means associated with said selective circuit for utilizingsaid changed carrier frequency current to operate a calling device.

6. In a system for signaling over a carrier current system, a highfrequency energy transfer circuit, a low frequency circuit associatedwith each terminal of said high frequency circuit, means interconnectingsaid circuits at one terminal of said high frequency circuit whereby lowfrequency impulses may be'transmitted from said low frequency circuitover said high frequency circuit as modulated carrier oscillations, saidmeans including a carrier frequency oscillator, means interconnectingsaid high frequency and low frequency circuits at the other terminal ofsaid high frequency circuit comprising demodulating means, a band filterin said high frequency circuit so de' changing the electrical conditionof said circuit.

8. The combination recited in claim 6 in which the carrier frequencyoscillator includes a frequency determining circuit having.a'capacitance and in which the means for changing the carrier frequencyconsists of a relay, a capacitive circuit in shunt with saidcapacitance, and circuit closing means in said capacitive circuitadapted to be actuated by said relay.

9. The combination recited in claim 6 in 10. In a carrier wavecommunication system having transmitting and receiving statrons, acarrier wave channel including at the transmitting station circuits forgenerating a carrier wave and for modulating the carrier wave inaccordance with message waves to be transmitted, and at the receivingstation circuits for demodulating the mes sage modulated wave toreproduce the message currents, said channel including also a bandfilter for selectively transmitting frequency components of the messagemodulated wave lying to one side of the said car; rier wave frequency inthe frequency spectrum while suppressing the components of the messagemodulated wave lying to the other side of said carrier wave frequency,means for transmitting signaling indications through said channelcomprising means at the transmitting station for changing the carrierfrequency to a level within the range of free transmission of saidfilter, means at the receiving station for selectively receiving thesaid wave of changed frequency and a signal device controlled by theselected wave.

11. In a signaling system, a transmitting station, a distant receivingstation having call signaling apparatus, a source for supplying carrierwaves of given frequency at said transmitting station, means to modulatesaid carrier waves in accordance with signaling waves whereby a band offrequencies adjacent said carrier Wave frequency is produced, means toselect and transmit the carrier and-the said band lying to one side ofthe carrier to the exclusion of other frequencies, and means at saidtransmitting station to change the carrier frequency to one within saidband of frequencies to operate said call signaling apparatus.

12. In a carrier wave signaling system, a source of speech'fr'equencycurrent, an electron discharge oscillator for' producing carriercurrent, a modulator whereby said carrier current is modulated inaccordance with current from said speech frequency current source,conductors extending between said speech frequency current source andsaid modulator, a condenser for determining the frequency produced bysaid oscillator, a second condenser associated with said first.mentioned condenser, and means actuated bycurrent flowing in saidconductors to change the manner of association of said second condenserwith respect to said first mentioned condenser to change the frequencyof the generated oscillations.

In witness whereof, I hereunto subscribe my name this 22 day of DecemberA. D., 1920.

JACOB S. JAMMER.

